Conventionally, as a cylindrical metal member used as a bush, there has been proposed a multi-layer slide member having a back metal layer consisting of, for example, a cylindrical steel plate and a porous layer formed on a surface of the back metal layer.
The porous layer is a structure made by filling a metallic porous member with a resin composition. In the case of a bush used for automobile parts, the metallic porous member is often made of a copper alloy. There is a case where lubricating oil contains a sulfur ingredient. The sulfur ingredient can corrode the metallic porous member made of the copper alloy and deteriorates durability of the metallic porous member.
Therefore, the material (copper (Cu)—tin (Sn) alloy) of the metallic porous member is impregnated with 21 to 35 mass % of nickel (Ni), thereby improving the corrosion resistance of the metallic porous member (refer to Patent document 1: JP-A-2011-80525).
As prior art documents relating to the present invention, Patent document 2 (JP-A-2001-220630) and Patent document 3 (JP-A-H08-53725) should be also referred to.
The metallic porous member is formed by sintering. Therefore, if high mass % (21 to 35 mass %) of Ni having the higher melting point than Sn and Cu is contained as a raw material of the metallic porous member as in the conventional technology, high sintering temperature is required for forming the metallic porous member. In addition, because Ni is expensive metal, it causes increase of production cost, coupled with the high sintering temperature.
Therefore, the inventors of the present invention have studied hard to provide a multi-layer slide member that has high corrosion resistance regardless of compounded quantity of Ni, or from another viewpoint.